TORUS employs two different methods to calculate the entry angle.

Method 1

For the Method 1 measurement, TORUS uses the following formula: q = q'/2, where q' is the actual acute angle, and q is the entry angle; to obtain the entry angle value, the actual angle value must be divided by two (see the Method 1 illustration below).

Entry Angle Measurement - Method 1

In the Method 1 calculation, the entry and exit radii are used. The lane midpoint for each radius is best fit with the curve that extends to the edge of the splitter island envelope. Lines AB and CD begin at the crossing of the best fit arc and the extended circulatory roadway side of the splitter island envelope, and then lines AB and CD are projected tangent from the best fit arc towards the circulatory roadway. The value of angle q' formed by the crossing of lines AB and CD is normally twice the value of entry angle q.

Method 2

According to Method 2, the entry angle is formed by the crossing of the tangent line projected from the entry width midpoint with the tangent line drawn along the middle of the circulatory roadway (see the Method 2 illustration below).

Entry Angle Measurement - Method 2

In the Method 2 calculation, the entry width is used. From the midpoint of the entry width, Line AB is projected perpendicular towards the circulatory roadway. Line CD begins at the crossing of the line AB and the arc located at the center of the circulatory roadway, and then line CD is projected tangent from the arc located in the center of the circulatory roadway. The angle formed by the crossing of the lines AB and CD is entry angle q.

Selecting an Appropriate Entry Angle Measurement Method

For the purposes of describing the software, it is assumed that Design Guidelines -> General: Traffic Direction is set to Right-Hand Traffic. If Traffic Direction is set to Left-Hand Traffic, the descriptions with references to a right/left turn path should be interpreted in the opposite direction.

You should use engineering judgment as you decide which entry angle measurement method to apply. The most commonly used approach to selecting an appropriate entry angle measurement method is based on the following criteria:

1. If the distance from the left side of the entry path to the left side of the next exit path does not exceed 100 feet, Method 1 is used (see Method 1).
2. If the distance from the left side of the entry to the left side of the next exit exceeds 100 feet, the actual angle value is used (see Method 2).
3. If there is no adjacent exit path, or if it is located at such a distance or an obtuse angle from the entry path that rendering the circulatory roadway is a dominant factor of the entry path, Method 2 is used (see Method 2).